Before you start
You need an HTTPS origin you control, the exact bytes of your terms of service, an Ed25519 keypair if you issue RP-signed receipts, and a place to store the account mapping.
What a conformant provider does
A conformant provider does four things: serve an identity-only /.well-known/agent-signup.json, verify the assertion against the broker's JWKS with every check in section 7.1, return the stable error codes, and optionally return an RP-signed receipt plus a hash-pinned context guide. An optional provider account adds a broker-issued verification credential, authenticated receipts, abuse standing, and the verified listing; it is not required to accept assertions.
Next
The step-by-step provider quickstart lives in the Providers section. The normative implementation guide is implementing-agent-identity-v1, and the validator checks a document before you publish it.